From an
insurance perspective, where the boat is registered is not important.
Insurance companies care about
Navigation Territory (where you are going to use the boat), your "regular
mooring address", and what your mailing address is. To that end, having a mailing address in the
USA (even if it's just a mail forwarding company, like Voyager mail forwarding) will allow you to get insurance through an American company. European Insurers will be fine with a Canadian, US, or European address.
I
work with both European and US
marine insurance companies, so when you're ready for a quote on insurance, send me an off-line message. Best of luck finding your dream boat,